1. Field of the Invention
The present invention relates to a system and method for controlling the speed of an engine in a vehicle.
2. Background Art
The operation of an engine in a vehicle can, at times, create undesirable noise and vibrations that detract from vehicle passenger comfort. This may be particularly true if the engine is allowed to operate at a frequency that is at or near the resonant frequency of a mechanical component or system within the vehicle. When this occurs, the vibrations in the mechanical system caused by the engine can increase significantly. To address this problem, at least one known vehicle predetermines allowable engine idle speeds such that the frequency of engine operation at these speeds will not match the resonant frequency of any of a chosen number of vehicle mechanical components and systems. In such a case, the allowable engine idle speed is a static value that is not adjusted in light of changing vehicle operating conditions.
One vehicle operating condition that may be of particular concern with regard to noise and vibration is the charging of a high voltage battery in a hybrid electric vehicle (HEV). When the high voltage battery in an HEV is charged, it effectively applies an extra load to the engine—this is known as lugging. When lugging occurs, certain vibration modes in the vehicle may be excited, and in general, noise and vibration levels in the passenger compartment may be amplified. Conventional engine idle control systems do not adequately address this issue, in that charging the high voltage battery can cause the engine to create undesirably high vibrations and noise even when the frequency is outside the resonant frequency range of the vehicle mechanical systems.
Therefore, a need exists for a system and method for controlling the speed of an engine that not only consider the resonant frequencies of various vehicle mechanical systems, but also consider noise and vibration when determining the engine speed.